In conventional practice, supermarkets and convenience stores are equipped with refrigerated merchandisers, which may be open or provided with doors, for presenting fresh food or beverages to customers while maintaining the fresh food and beverages in a refrigerated environment. Typically, cold, moisture-bearing air is provided to a product display area of the merchandiser by passing an airflow over the heat exchange surface of an evaporator coil, or evaporator. A suitable refrigerant is passed through the evaporator, and as the refrigerant evaporates while passing through the evaporator, heat is absorbed from the air passing through the evaporator. As a result, the temperature of the air passing through the evaporator is lowered for introduction into the product display area of the merchandiser.
Such a prior-art refrigerated merchandiser 10 is shown in FIG. 1. The merchandiser 10 includes a case 14 generally defining an interior bottom wall 18, an interior rear wall 22, and an interior top wall 26. The area bounded by the interior bottom wall 18, interior rear wall 22, and the interior top wall 26 defines a product display area 30, in which the fresh food and/or beverages are stored on one or more shelves 32. The case 14 includes an open front face to allow customers access to the fresh food and/or beverages stored in the case 14.
The case 14 also generally defines an exterior bottom wall 34 adjacent the interior bottom wall 18, an exterior rear wall 38 adjacent the interior rear wall 22, and an exterior top wall 42 adjacent the interior top wall 26. A lower flue 46 is defined between the interior and exterior bottom walls 18, 34 to allow for substantially horizontal airflow throughout the lower flue 46. The interior bottom wall 18 includes an opening 50 to communicate with the lower flue 46 to allow surrounding air to be drawn into the lower flue 46. A rear flue 54 is defined between the interior and exterior rear walls 22, 38 and is fluidly connected with and adjacent to the lower flue 46. The rear flue 54 allows for substantially vertical airflow throughout the rear flue 54. An upper flue 58 is defined between the interior and exterior top walls 26, 42 and is fluidly connected with and adjacent to the rear flue 54. The upper flue 58 allows for substantially horizontal airflow throughout the upper flue 58. The interior top wall 26 includes an opening 62 to communicate with the upper flue 58 to allow airflow in the upper flue 58 to be discharged from the upper flue 58. When combined, the lower flue 46, the rear flue 54, and the upper flue 58 comprise an air passage separate from the product display area 30.
The refrigerated merchandiser 10 also includes some components of a refrigeration system (not entirely shown) therein. One or more fans 66 are located within the lower flue 46 toward the back of the case 14 to generate an airflow through the lower, rear, and upper flues 46, 54, 58. A conventional round-tube plate-fin evaporator 70 is located within the rear flue 54 toward the bottom of the case 14. The evaporator 70 is positioned downstream of the fans 66 such that the airflow generated by the fans 66 passes through the evaporator 70. The fans 66 may also be positioned upstream of the evaporator 70. The refrigeration system may also include other components (not shown), such as one or more compressors, one or more condensers, a receiver, and one or more expansion valves, all of which may be remotely located from the refrigerated merchandiser 10.
The evaporator 70 is configured to receive a liquid refrigerant from the receiver. As is known in the art, the liquid refrigerant is evaporated as it passes through the evaporator 70 as a result of absorbing heat from the airflow passing through the evaporator 70. Consequently, the temperature of the airflow passing through the evaporator 70 decreases as it passes through the evaporator 70. The heated, or gaseous refrigerant then exits the evaporator 70 and is pumped back to the remotely located compressor(s) for re-processing into the refrigeration system.
With reference to FIG. 1, the interior rear wall 22 includes a plurality of apertures 74 formed therein. The apertures 74 are centrally located in the interior rear wall 22, and fluidly connect the product display area 30 and the rear flue 54. The apertures 74 allow some of the refrigerated air in the rear flue 54 to exit the rear flue 54 and enter the product display area 30. Products located in the product display area 30 may then be cooled by the refrigerated air.
The remaining portion of the refrigerated airflow that does not pass through the apertures 74 is routed vertically through the rear flue 54, and horizontally through the upper flue 58 before being discharged from the upper flue 58 via the opening 62 in the interior top wall 26. After being discharged from the opening 62 in the interior top wall 26, the refrigerated airflow moves downwardly along the open front face of the refrigerated merchandiser 10 before being drawn back into the opening 50 in the interior bottom wall 18 for re-use by the fans 66. This portion of the refrigerated airflow is known in the art as an air curtain 78. The air curtain 78, among other things, helps maintain the air temperature in the product display area 30 within a standard temperature range of 32° F. to 41° F. determined by the Food and Drug Administration (“FDA”) Food Code for potentially hazardous foods.
As shown in FIG. 1, the size of the conventional round-tube plate-fin evaporator 70 often requires the fans 66 to be positioned in the lower flue 46 beneath the product display area 30. As a result, the fans 66 occupy valuable space in the merchandiser 10 that could otherwise be used for storing additional food and/or beverage products. Further, spilled product from the product display area 30 may come into contact with the fans 66, thus making cleanup of the merchandiser 10 more difficult.
Also, in some prior-art refrigeration cases (not shown), the evaporator is located in the lower flue along with the fans beneath the product display area of the merchandiser. As a result, complex ducting structure is usually required in the rear flue to route the airflow passing through the evaporator to different regions within the product display area. Also, spilled products from the product display area may come into contact with the evaporator, thus making cleanup of the merchandiser more difficult.
In conventional practice, evaporators 70 utilized in medium-temperature refrigeration merchandisers 10, such as those commonly used for displaying produce, meats, milk and other dairy products, or beverages in general, generally operate with refrigerant temperatures well below the freezing point of water (i.e., 32° F.). Further, the airflow generally exits the evaporators 70 at a temperature below the freezing point of water. Thus, during operation of the merchandisers 10, frost often forms on the evaporators 70 as a result of moisture in the air condensing onto the evaporator 70 and freezing.
Such medium-temperature refrigerated merchandisers 10 operate in this manner because the refrigerated products, like produce, meats, and dairy products, must be maintained in an environment whereby the temperature is maintained in the 32° F. to 41° F. range determined by the FDA. For the prior-art merchandisers 10 to achieve these temperatures in their product display areas 30, the refrigerant passing through the conventional round-tube plate-fin evaporators 70 is maintained at a saturation temperature of about 24° F. The resultant airflow passing through the evaporator 70 is cooled to about 31° F. At these outlet temperatures, moisture in the airflow will condense out of the airflow, settle on the evaporator 70, and freeze since the evaporator 70 is maintained at a temperature below the freezing point of water, thus leading to the build-up of frost on the evaporator 70. As frost builds up on the evaporator 70, the performance of the evaporator 70 deteriorates, and the free flow of air through the evaporator 70 becomes restricted and in extreme cases halted.
The conventional round-tube plate-fin evaporators 70 characteristically have a low fin density, typically in the range of 2 to 4 fins per inch. This practice arises in anticipation of the buildup of frost of the surface of the evaporator 70 and the desire to extend the period between required defrosting operations. As frost builds up, the effective flow space for air to pass between neighboring fins becomes progressively less and less until, in the extreme case, the space is bridged with frost. As a consequence of frost buildup, the evaporator's performance decreases, and the flow of adequately refrigerated air to the product display area 30 decreases, thus necessitating activation of a defrost operation. Typically, several defrost operations are required per day to eliminate the accumulated frost on the evaporator 70. Performing the defrost operations may be detrimental to the food and/or beverage products, since the products may be allowed to warm-up to a temperature above the 32° F. to 41° F. temperature range determined by the FDA. Defrosting the evaporator 70 also typically results in increased energy expenditures, since a relatively large amount of energy is required to initially “pull down” the air temperature in the product display area 30 after a defrost operation to an acceptable temperature within the 32° F. to 41° F. range.
As a result of their inherent inefficiencies, conventional round-tube plate-fin evaporators 70 are often physically large, and are often mounted in the merchandiser 10 such that the airflow passing through the evaporator 70 is required to pass through the evaporator 70 in a direction coinciding with a major dimension (i.e., the length or height) of the evaporator 70 to achieve the desired airflow temperature exiting the evaporator 70 and the desired air temperature in the product display area 30 of the merchandiser 10. The airflow is passed through the evaporator 70 in a direction coinciding with the major dimension to allow the evaporator 70 sufficient time to remove enough heat from the airflow to cool the airflow to a temperature of about 31° F. Further, the apertures 74 in the interior rear wall 22 are required to be centrally located, since the height of the evaporator 70 dictates the location of the apertures 74. This prevents refrigerated air from reaching products situated in a lower portion 80 of the product display area 30.